Pakistan, Aug. 3 -- Extremism rarely begins with a bomb. Long before violence reaches a checkpoint, a marketplace or a place of worship, an intellectual boundary has usually been crossed. Political disagreement is turned into religious excommunication, institutional criticism becomes rejection of the state itself, and those who think differently are gradually transformed from opponents into enemies and eventually into supposedly legitimate targets.

This progression is particularly important for Pakistan, where terrorism is not merely a contest of arms. It is also a contest over ideas: who possesses religious legitimacy, who may define jihad, whether a constitutional state can be declared un-Islamic by private groups, and whether individu...